We investigated electron doping of monolayer hexagonal boron nitride (hBN) on metallic substrates by doping alkali metals (AMs). The valence band maximum (VBM) of hBN/Rh after doping with Li and Cs was directly observed using angle-resolved photoemission spectroscopy in a wide wavenumber space. The valence band shift resulting from doping confirms the vacuum level alignment model. Furthermore, when the same AM is used, the resultant binding energy of VBM was almost identical regardless of the substrate, even if it differs by ∼1 eV before doping, which we found by comparison with the literature. This independence from the substrate is explained by an extension of the vacuum level alignment model, wherein the VBM is determined by the work function of the AM when it intercalates to the interface as well as adsorbs on surfaces of hBN. It means that the doping of Cs, which has the lowest work function, gives the deepest binding energy at VBM. This is evaluated as 5.7 eV in our experiments.

Ultra-short, low-loss graphene-organic hybrid phase modulators are introduced. 20 Gbit/s PAM-2 and PAM-4 data modulation are demonstrated with devices of 25 μm length and on-chip losses of 0.86 dB.

Endohedral fullerenes, such as Dy2ScN@C-80, are single-molecule magnets with long relaxation times of their magnetization. An open and anisotropic 4f electron shell in the lanthanides (here Dy) imposes a magnetic moment that maintains its orientation at liquid-helium temperatures for macroscopic times. If these molecules shall be used as single-bit information storage elements or for quantum operations, the orientation of the endohedral units and the orientation of the magnetic moments has to be controlled. X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD)-with variation of the angle of x-ray incidence-allows for the detection of these two structural elements. We present XMCD data of Dy2ScN@C-80 on an h-BN/Rh(111) nanomesh that display at 2 K a large hysteresis with a coercive field of 0.4 T. The angular dependence of the XAS data at the Dy M-5 edge indicates partial ordering of the endohedral units. In order to quantify anisotropic orientation we introduce the "deviation" D as an operational quantity that measures differences between two spectra.

T. Greber,1 A. P. Seitsonen,2 A. Hemmi,1 J. Dreiser,3 R. Stania,1 F. Matsui,4 M. Muntwiler,3 A. A. Popov,5 and R. Westerström6 1Physik-Insitut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland 2Département de Chimie, École Normale Supérieure, 24 Rue Lhomond, F-75005 Paris, France 3Paul Scherrer Institut, CH-5232 Villigen, Switzerland 4Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma, Nara 630-0192, Japan 5Leibniz Institute of Solid State and Materials Research, Helmholtzstraße 20, D-01069 Dresden, Germany 6Division of Synchrotron Radiation Research, Lund University, SE-22100 Lund, Sweden

The setup of an apparatus for chemical vapor deposition (CVD) of hexagonal boron nitride (h-BN) and its characterization on four-inch wafers in ultra high vacuum (UHV) environment is reported. It provides well-controlled preparation conditions, such as oxygen and argon plasma assisted cleaning and high temperature annealing. In situ characterization of a wafer is accomplished with target current spectroscopy. A piezo motor driven x-y stage allows measurements with a step size of 1 nm on the complete wafer. To benchmark the system performance, we investigated the growth of single layer h-BN on epitaxial Rh(111) thin films. A thorough analysis of the wafer was performed after cutting in atmosphere by low energy electron diffraction, scanning tunneling microscopy, and ultraviolet and X-ray photoelectron spectroscopies. The apparatus is located in a clean room environment and delivers high quality single layers of h-BN and thus grants access to large area UHV processed surfaces, which had been hitherto restricted to expensive, small area single crystal substrates. The facility is versatile enough for customization to other UHV-CVD processes, e.g., graphene on four-inch wafers.

The construction of an alkali-metal ion source is presented. It allows the acceleration of rubidium ions to an energy that enables the penetration through monolayers of graphene and hexagonal boron nitride. Rb atoms are sublimated from an alkali-metal dispenser. The ionization is obtained by surface ionization and desorption from a hot high work function surface. The ion current is easily controlled by the temperature of ionizer. Scanning Tunneling Microscopy measurements confirm ion implantation.